Balance Your Black and White Values
When printing images it’s important to make sure your blacks don’t contain too much ink, and it’s also important that your white areas aren’t blown out so the CMYK ink value is 0-0-0-0. To ensure this, you can set the white and black values for your image, making the set value for black slightly lighter, and the set value for white slightly darker. Here’s how you do it:
With your image open, add a threshold adjustment layer.
Zoom in to one of these black spots. With the eye-dropper tool, shift-click on one of these remaining black spots. You’ll see it leaves a little crosshair icon with the number 1 next to it. You can’t see it in the image below, but the center of the crosshair is directly over a black pixel.
Turn off the threshold adjustment layer, or delete it – you don’t need it anymore.
Add a curves adjustment layer to your image.
Double click the black eye-dropper tool on the curves adjustment panel to get your “target shadow colour” window.
Set the brightness to 5 (H=0, S=0, B=5) then, with the black eye-dropper tool still selected, alt/option+click on the dark point you set on your image (number 1). Zoom in to click on that spot exactly.
Double click the white eye-dropper in the curves panel and change the brightness to 95 (H=0, S=0, B=95), and then alt/option+click (with your white eye-dropper tool still selected) the light point you set on your image.